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Are women really stronger than men? | Angela Saini

When it comes to longevity, surviving illness and coping with trauma, one gender comes out on top. Angela Saini meets the scientists working out why

Four years ago, completely spent, blood transfused into me in a frantic effort to allow me to walk, I lay on a hospital bed having given birth the day before. To the joy of my family, I had brought them a son. Blue balloons foretold a man in the making. Not just the apple of my eye, but the one who would one day open jam jars for me. The hero who would do the DIY and put out the rubbish. He who was born to be strong because he is male.

But then, physical strength can be defined in different ways. What I was yet to learn was that, beneath our skin, women bubble with a source of power that even science has yet to fully understand. We are better survivors than men. Whats more, we are born this way.

Pretty much at every age, women seem to survive better than men, says Steven Austad, an international expert on ageing, and chair of the biology department at the University of Alabama. For almost two decades, he has been studying one of the best-known yet under-researched facts of human biology: that women live longer than men. His longevity database shows that all over the world and as far back as records have been kept, women outlive men by around five or six years. He describes them as being more robust.

Robustness, toughness or pure power whatever its called this survival ability cracks apart the stereotype. The physically strong woman is almost a myth. We gaze upon great female athletes as though theyre other-worldly creatures. Greek legend could only imagine the Amazons, female warriors as powerful as men. They break the laws of nature. No, we everyday women, we have just half the upper body strength of men. We are six inches shorter, depending on where we live. We wield power, but its emotional and intellectual, we tell ourselves. Its not in our bodies.

Not so, says Austad. He is among a small cadre of researchers who believe that women may hold the key to prolonging life. In extremely old age, the gap between the sexes becomes a glaring one.

According to a tally maintained by the global Gerontology Research Group, today, 43 people around the world are known to be living past the age of 110. Of these supercentenarians, 42 are women. Interviews with the worlds current oldest person, 117-year-old Violet Brown, who lives in Jamaica, reveal she enjoys eating fish and mutton. She once worked as a plantation worker. Her lifestyle betrays few clues as to how she has lived so long. But one factor we know has helped is being a woman.

But if they receive exactly the same level of care, males are statistically at a 10% greater risk than females. What makes baby girls so robust remains mostly a mystery. Research published in 2014 by scientists at the University of Adelaide suggests that a mothers placenta may behave differently depending on the sex of the baby, doing more to maintain the pregnancy and increase immunity against infections. For reasons unknown, girls may be getting an extra dose of survivability in the womb.

Wherever it comes from, women seem to be shielded against sickness later on. Cardiovascular disease occurs much earlier in men than women. The age of onset of hypertension [high blood pressure] also occurs much earlier in men than women. And theres a sex difference in the rate of progression of disease, says Kathryn Sandberg, director of the Centre for the Study of Sex Differences in Health, Ageing and Disease at Georgetown University.

Austad found that in the United States in 2010, women died at lower rates than men from 12 of the 15 most common causes of death, including cancer and heart disease, when adjusted for age. Of the three exceptions, their likelihood of dying from Parkinsons or stroke was about the same. And they were more likely than men to die of Alzheimers disease. Once I started investigating, I found that women had resistance to almost all the major causes of death, he says.

If they are right, this raises a deeper scientific conundrum. Our bodies adapted over millennia to our environments. So what could it have been in our evolutionary past that gave the female body a little more of this magical robustness? How and why would one sex have developed a survival edge over the other?

Studies of hunter-gatherer societies, who live the way we all may have done before fixed settlements and agriculture, provide a few clues. Many anthropologists studying tribal communities in Africa, South America, Asia and Australia believe early humans lived fairly equal lives, sharing responsibility for food, shelter and raising children. The Flintstones model, with wife at home and husband bringing back the bacon, just doesnt stand up. Instead, the evidence shows that women would have done at least the same physical work as men, but with the added burden of bearing children.

Theres a general consensus now that hunting-gathering societies, while not perfectly egalitarian, were less unequal, particularly with regard to gender equality, says Melvin Konner, professor of anthropology at Emory University in Atlanta, who has spent years doing fieldwork with hunter-gatherers in Africa. Because of the scale of the group dynamics, it would be impossible for men to exclude women.

The more research that is done, the more this is reinforced. Even hunting that prototypical male activity is being recast as a female one, too. Anthropologist Rebecca Bliege Bird, a professor at Pennsylvania State University, offers me the example of the Martu, an aboriginal tribe in Western Australia. When Martu women hunt, one of their favourite prey are feral cats. Its not a very productive activity, but its a chance for women to show off their skill acquisition.

Indeed, women are known to be particularly good at endurance running, notes Marlene Zuk, who runs a lab focusing on evolutionary biology at the University of Minnesota. In her 2013 book Paleofantasy, she writes that womens running abilities decline extremely slowly into old age. Theyve been known to go long distances even while pregnant. In 2011, for example, Amber Miller ran the Chicago marathon before giving birth seven hours later. World record holder Paula Radcliffe has trained through two pregnancies.

Why, then, are we not all Amazons? Why do we imagine femininity to mean small, waif-like bodies? The lives of most ordinary women, outside the pages of magazines, destroy this notion. Visiting Indias cities, I see female construction workers lining the streets, hauling piles of bricks on their heads to building sites. In Kenya, I meet female security guards everywhere, patrolling offices and hotels. Out in rural areas, there are women doing hard physical labour, often hauling their children in slings. Our ancestors would have done the same.

In evolutionary terms, these were the circumstances under which our bodies were forged. For an enormous chunk of early human history, as we migrated through Africa to the rest of the world, women would also have travelled hundreds or thousands of miles, sometimes under extreme environmental conditions. Just reproducing and surviving in these conditions, talk about natural selection! Im told by Adrienne Zihlman, an anthropologist at the University of California, Santa Cruz, when I visit her at her home in San Francisco.

Zihlman has dedicated her career to understanding human anatomy, and in particular the evolution of womens bodies. Women have to reproduce. That means being pregnant for nine months. Theyve got to lactate. Theyve got to carry these kids. Theres something about being a human female that was shaped by evolution. Theres a lot of mortality along the way that really can account for it.

When I gave birth to my son, I did the most physically demanding thing a human can do. Yet I am considered the weaker sex. Zihlman reminds me that my body was made strong by the struggles of countless generations of women who went before. There is something about the female form, the female psyche, just the whole package, that was honed over thousands and thousands, even millions, of years to survive, she smiles. I happen to remember, in that moment, that at home I do all the DIY.

Myths and misses: five more things you didnt know about women and men

Separate symptoms Women and men present different symptoms for the same medical conditions. Women are more likely to have insomnia and fatigue in the weeks before they have a heart attack, rather than the chest pain commonly experienced by men.

Changes of life Women in India, Japan and China experience far fewer menopause symptoms than western women who commonly report hot flushes, night sweats, depression and insomnia. Scientists at Kings College London argue this could be due to women lumping together their experience of growing older with the menopause.

Casual sex Women are choosier but not more chaste than men. A study by two German researchers, Andreas Baranowski and Heiko Hecht, found that women want casual sex just as much as men and were as likely as males to have sex with a stranger, as long as it was in a safe environment.

Boys toys A 2010 study by Professor Melissa Hines at the University of Cambridge found that girls on average were genetically predisposed to prefer dolls while boys liked to play with mechanical toys such as trains.

Risky business Testosterone is associated with higher levels of optimism, rather than aggression. Saliva samples taken from traders on the London Stock Exchange confirmed they had higher than average testosterone levels. Scientists from Britain, the USA and Spain concluded this increase made the traders more optimistic so more likely to take big financial risks.

Inferior: How Science Got Women Wrong and the New Research Thats Rewriting the Story by Angela Saini is published by Fourth Estate at 12.99. To order a copy for 11.04, go to bookshop.theguardian.com